Aluminum is known to be used in bicycle frames because of its light weight and good strength properties. In general, a bicycle frame is made by joining several tube-type members together which can be by tube and socket joining or, in modern bicycle frames, by welding. The frames can also be assembled by adhesive or other bonding or by combinations of these and other joining techniques. In general, aluminum frames have larger diameter tubes with thinner walls than tubes for steel frames. Aluminum alloys offer obvious advantages in high performance or racing bicycles and have been used in those applications for a number of years. In addition, aluminum frames have some flex which can be advantageous for impact and shock resistance. Some bicycles can be of a single permanent rigid frame or they can have a main or core frame plus subframe parts or assemblies especially where the bicycle includes moving suspension members.
Aluminum alloy 5086-H32 has been used in bicycle frames for a number of years. Alloy 5086 is a non-heat treatable alloy that has a relatively high ultimate tensile (breaking) strength which is important in a bicycle frame, but suffered a reduction in its yield strength in the heat affected zones adjacent weldments. Despite this low to modest yield strength disadvantage, it was employed for a number of years because of its good ultimate strength. Alloy 5086, according to the Aluminum Association registration, the entire contents of which are incorporated herein by reference, contains 3.5 to 4.5% magnesium, 0.2 to 0.7%% manganese, 0.05 to 0.25% chromium, 0.4% maximum silicon, 0.5% maximum iron, 0.1% maximum copper, 0.25% maximum zinc, the balance aluminum and incidental elements and impurities.
Another aluminum alloy tube product that has been used in making bicycles is alloy 7005. This alloy is a heat treatable alloy and has good T6 temper strength, including good strength in heat affected zones adjacent welds provided the bicycle frame was heat treated and artificially aged after welding, so as to offer some advantage over the 5086-H32 product. However, alloy 7005 has a lower corrosion resistance and stress corrosion cracking resistance level than alloy 5086. Alloy 7005 could be provided as F temper or O temper tube with end regions thickened by butt forming and welded to make the bicycle frame which was then solution heat treated and air-quenched and artificially aged to good strength levels. Another practice could include starting with artificially aged T62 or T63 temper. Alloy 7005, according to Aluminum Association registration, contains 4 to 5% zinc, 0.2 to 0.7% manganese, 1 to 1.8% magnesium, 0.06 to 0.2% chromium, 0.08 to 0.2% zirconium, 0.01 to 0.06% titanium, maximum of 0.35% silicon, 0.4% maximum iron, 0.1% maximum copper, the balance aluminum and incidental elements and impurities.
Another aluminum alloy tube product that has been employed in bicycle frames is alloy 6061-T6. This alloy offered good strength, together with good corrosion resistance, and could have good strength properties in heat affected zones adjacent weldments provided the bicycle frame was re-heat treated after welding. This required solution heat treating the entire bicycle frame and quenching it which, in turn, typically distorted the frame such that it had to be straightened at some not insignificant cost. The frame was then artificially aged to T6 temper. Alloy 6061, according to Aluminum Association registration limits, contains 0.8 to 1.2% magnesium, 0.4 to 0.8% silicon, 0.15 to 0.4% copper, 0.04 to 0.35% chromium, 0.7% maximum iron, 0.15% maximum manganese, 0.25% maximum zinc, the balance aluminum and incidental elements and impurities.
Each of the above-mentioned alloys has found substantial use in making aluminum bicycle frames and each has served reasonably well for that purpose, but there is room for improvement.